(a) Field of the Invention
The present invention relates to a method for recording data on an optical disk by using a running optimum power control (OPC) technique and, more particularly, to a technique for recording data on an optical disk by controlling the recording optical power based on the results of detection of the recorded state of data (mark) on the optical disk. Th present invention also is relates to an optical disk drive using the running OPC technique.
(b) Description of the Related Art
Known parameters representing the recorded state of the mark recorded on the track of an optical disk include “asymmetry” and “β”, which represent the asymmetry of the waveform of the radio frequency (RF) signal reproduced from the optical spot reflected from the mark on the optical disk.
FIG. 10 exemplifies a graph of the power margin characteristic showing the relationship between the parameter β (%) and the jitter of the RF signal. It is shown therein that the jitter of the RF signal exceeds a threshold Th if the parameter β deviates from a suitable range. In FIG. 10, the power margin shown therein corresponds to the range of the parameter β (or asymmetry instead), which provides an allowable value for the jitter, i.e., below the threshold Th.
The power margin has a significant range of variation depending on the type of the optical disk. If the optical disk has a narrow range of power margin, it is required that the parameter β or asymmetry be more uniform and stable over the entire recording area of the optical disk, because a larger range of fluctuation in the parameter β or asymmetry causes a serious problem. Recently, along with the development of higher speed recording on the optical disk, there is a tendency of reduction of the power margin for the optical disk, thereby requiring more uniform and stable value for the parameter β over the entire recording area of the optical disk.
In the mean time, for achieving the higher speed recording, a zone-constant linear velocity (Z-CLV) recording scheme or constant angular velocity (CAV) recording scheme is generally used, which causes, however, a difficulty in the power control so as to obtain a suitable recorded state providing a uniform and stable parameter for β.
In the circumstances as described above, an optimum power calibration technique is generally used wherein trial data recording is performed in a selected power calibration area of the optical disk before actually recording desired data. The desired data is recorded on the recording area of the optical disk by using the fixed level of the optimum recording power obtained by the optimum power calibration technique.
In the optimum power control (OPC) technique, there may arise problems such that the characteristic of the optical disk fluctuates within the recording area, that the plane of the recording surface fluctuates due to radial skew or warp of the optical disk, that the OPC recording causes a temperature change of the optical disk to change the characteristic thereof, and that the V-CLV or CAV recording technique involves a velocity fluctuation during the OPC recording. Such problems do not provide an optimum recorded state irrespective of employing the OPC recording scheme.
For solving the above problems in the conventional techniques, a technique using a running OPC recording scheme is proposed wherein the recorded state is detected while the recording is performed on the optical disk by using a variety of techniques, thereby correcting the recording optical power based on the detected recorded state to maintain the optimum recorded state while running or continuing the recording.
Patent Publication JP-A-10-40548, for example, describes a running OPC recording technique wherein a maximum light intensity and a sampled light intensity of the optical spot reflected from a plurality of pits (marks) are detected over several frames in the actual recording area at the start of recording, a reference maximum light intensity and a reference sampled light intensity are then determined based on these detected intensities, and the laser power is corrected based on the results of comparison of a maximum light intensity and a sampled light intensity detected during the OPC recording against the reference maximum light intensity and the reference sampled light intensity, respectively, thereby achieving an accurate correction.
In the running OPC recording technique described in JP-A-10-40548, the reference maximum light intensity and the reference sampled light intensity are determined in the actual recording area, and used as fixed levels in the actual recording area, as described above. This causes a difficulty in controlling the recording optical power to obtain a stable and uniform recorded state in the whole actual recording area if the optical disk has a significant rage of variation in the disk characteristics or the plane of the disk surface fluctuates due to the inclined pivotal axis or warp of the disk.
JP Patent Application 2001-018620 proposes another running OPC recording technique wherein a signal representing the sum of the reflected optical power of the main beam is detected, and the stable level (Sp) of the reflected optical power obtained from the rear portion of the pit during the recording, the space level (Ss) of the reflected optical power obtained from the space during the recording and the power level of the laser at the objective lens are used as parameters for detecting the recorded state of the mark during the running OPC recording on the optical disk.
In the another running OPC recording technique described in JP Patent Application 2001-018620, since the space level (Ss) is used for correcting the fluctuation of the stable level (Sp) caused by fluctuation of the reflectivity of the disk, a stable reproducing power level is required during the recording operation for obtaining a stable correction. However, the reproducing power level, i.e., the reproducing optical power at the exit of the objective lens which is relatively low so as not to form a pit, is difficult to control at a fixed level due to an insufficient frequency characteristic of the front monitor. Thus, under the condition where the recording velocity changes, as in the case of Z-CLV or CAV recording scheme, the reproducing power level cannot be well controlled during the recording.
JP Patent Application 2001-020097 proposes another running OPC recording technique wherein side beams (sub-beams) are used instead of the main beam to obtain the parameters for detecting the recorded state during recording the data on the optical disk. In this technique, the recording optical power is controlled based on the ratio between the intensity of the front side beam and the intensity of the rear side beam, in view that the front side beam incident onto the unrecorded areas of the subject track and the adjacent outer track is reflected therefrom and the reflected beam is subjected to diffraction by the recorded pit and that the reflected beam of the rear side beam is subjected to the diffraction by the recorded pit.
In the technique described in Patent Application 2001-020097, since the side beams are used as the parameter for detecting the recorded state, there arises a problem in that the target value for the running OPC recording cannot be measured sometimes. More specifically, if the optical disk is a CD-R, it is prescribed that the OPC recording technique use test areas in the order from the peripheral area toward the central area without using the actual recording area. Thus, since the test area for the OPC test recording may be located adjacent to another test area for which OPC test waveform has been recorded, the front side beam is affected by diffraction only by the recorded track and not by the unrecorded area, whereby there is a difference between the cases of the OPC recording and the actual recording on the recording area. In addition, since the side beams are located between adjacent groove tracks to be recorded, or since a de-track amount may vary the amount of affection by diffraction by the adjacent track, the track pitch of the optical disk may be varied between the central area and the peripheral area of the disk, thereby preventing the stable running OPC recording.
It is to be noted that the running OPC technique of the present invention also uses well-known standard technologies such as described in JP-A-2001-351242 for recording data on the optical disk in addition to the technologies in the running OPC techniques as described above.